The present invention relates to a coating system, and more particularly, to a coating station having a coating source and an oppositely situated workpiece carrier arrangement which has planet receiving devices for at least one respective workpiece centered with respect to the planet axis.
It is known to apply thin layers on substrates with different radii of curvature, as particularly to optical or ophthalmic lenses, by thermal vaporizing, electron beam vaporizing or by sputter coating, thus particularly by planar magnetrons. Planar magnetron sputtering is a coating process which has proven its excellent suitability for the automated individual substrate coating in numerous applications, as, for example, for CD-coating or for semiconductor manufacturing.
In the known case, a plurality of substrates are coated simultaneously as so-called "batches". The batch sizes vary from ten substrates to several hundred substrates. Often, as particularly in the manufacturing of ophthalmic lenses where different lens materials (glass types and plastics) must be treated with different coating formulas, this is a considerable disadvantage because, in each case, a sufficient number of substrates with the same coating formula must be collected in order to complete a batch.
In the past, single or multi-layer systems have been applied as optical coatings, for example, with changing refraction indices. Customary materials for this purpose are, in particular, dielectric materials such as SiO.sub.2, Si.sub.3 N.sub.4, etc. That is, especially in the case of optical or ophthalmic lenses, the variety of formulas is very large.
Systems for evaporation coating are generally large and complex which sometimes results in economic operation only with large batches.
In addition, optical and ophthalmic lenses may have very different positive or negative curvatures. Even in this case, optically effective coatings on such lenses must have a very uniform layer thickness distribution, with fluctuations typically being in the range of .+-.1%. With known evaporation process batch systems, this is achieved by arranging the substrates, that is, the lenses, at a large distance from the evaporation source on calotte-shell-shaped concave substrate carriers where the coating particles virtually everywhere impact on the areas to be coated at a right angle. For the individual coating or the coating of lenses in pairs, such an approach is not very suitable. Furthermore, it cannot be easily automated.
"Thin Film Processes", John L. Vossen, et al., Academic Press, Inc., page 147, describes the process of arranging lenses for coating thereof opposite a planar magnetron, specifically on a workpiece carrier planet arrangement in the case of which the lenses are rotated centrically with respect to the respective planet axes and revolve simultaneously with the sun system.
With respect to a revolving or planet arrangement, everything revolving only about the central axis of the system--the sun system axis--is called the "sun system" in the following. The "planetary system" revolves about the central axis as well as about one planet axis respectively.
The workpiece carrier planet arrangement or the substrate deposited thereon open up a surface which faces the sputter source area in a concave manner. The sputter source acts essentially as a point source into the calotte shell. Because of the calotte shell shape of the workpiece carrier planet arrangement and the respective centric magnetron arrangement, workpiece areas situated centrically closest to the sun system axis have identical shortest distances to the magnetron surface, such as workpiece and substrate areas passing through on the extreme outside with respect to the sun system axis.
This coating technique, which is schematically shown in the above-mentioned document, has the disadvantage that the achievable layer thickness distribution does not meet the above-mentioned requirements.
In "Planetary System for High Uniformity Deposited Layers on Large Substrates", A. Perrin, et al., SPIE Vol. 1782, "Thin Films for Optical Systems" (1992), pp 238-244, the coating of large substrates (.phi. 300 mm) by a vaporization source (crucible) operating in a punctiform manner is described. For a good layer thickness distribution, a substrate carrier planet arrangement is convexly placed against the vaporization source which is shifted with respect to the sun system axis. The distance perpendicularly between the vaporization surface and the rotational centers of the planets is larger than the diameter of the sun system.
The disadvantage of this known approach is the decentralized position of the vaporization source which has the result that the vaporization rate varies with the rotary frequency of the sun system and the vaporization process is therefore relatively poorly utilized. In addition, the corresponding system is relatively voluminous because the required punctiformity of the source is ensured only in the case of the above-mentioned relatively large distance between the source and the moving path of the substrates on the planets.
It is an object of the present invention to provide a coating station by way of which a small number of substrates with a surface, which is arbitrarily curved within wide limits and is to be coated, can be coated as economically as possible, specifically with a good layer thickness distribution within wide limits also independently of the operating duration of the source. In this case, the station should be as compact as possible and the process should be easily implementable.
The foregoing objects have been achieved by providing a station in which the coating source is a flat sputter source having an area centered at least in one dimension thereof with respect to a sun system axis, and the planet arrangement and the sputter source are configured such that a shortest distance between a workpiece area which is outermost with respect to the sun system axis and a new surface of the sputter source is larger than a shortest distance between a workpiece area which is innermost with respect to the sun system axis and the new surface of the sputter source.